1. Field of the Invention
The present invention relates to members with which an ink comes into contact, namely to ink-contacting members, such as an ink-absorbing member, ink tank and ink cartridge, and an ink-jet recording apparatus utilizing the above.
2. Related Background Art
An ink-jet recording apparatus has heretofore had a general construction that an ink tank for storing an ink therein, and an ink ejection part for ejecting the ink from the ink tank are connected to each other directly or through an ink-feeding member such as a tube. In such an ink-jet recording apparatus, members always coming into contact with an ink are required to have an excellent resistance to corrosion from the ink and not to cause such deterioration in performance as impurities in the members are dissolved out in the ink during long-term storage to deteriorate the performance of the ink or as the members themselves react with the ink to become fragile.
As a material for forming the ink tank, there has heretofore been used a resin material, metallic material, rubber material or the like. Of these materials, a polyolefin, which is a resin material, has been preferably used from the viewpoints of cost, processability, resistance to chemicals and easy recycling. Examples of the polyolefin include polypropylene and polyethylene. A catalyst such as the Ziegler-Natta catalyst is generally used in polymerization of an olefin upon the production of these polyolefins, and so a catalyst residue such as a chlorine compound remains in a polymer formed. The catalyst residue remaining in the polymer has a possibility of corroding or deteriorating the polymer. For example, it may cause yellowing of the polymer. Therefore, it is common to add a neutralizer into the polymer for allowing the neutralizer to react with the catalyst residue to neutralize it.
As the neutralizer, calcium stearate has heretofore been used very widely. The neutralizer is generally added in an amount of from 1,000 to 1,500 ppm to the polymer though the amount varies according to the grade or the like of the polymer. As disclosed in Japanese Patent Application Laid-Open Nos. 62-60653 and 63-216752, it has however been known that this calcium stearate reacts with a sodium ion contained in an ink while being in contact with the ink for a long period of time to form a fibrous suspended matter, and the suspended matter causes a problem of impeding the flowability of the ink. In order to solve such a problem, there has been proposed a method in which calcium carbonate or magnesium carbonate is used as a neutralizer (refer to Japanese Patent Application Laid-Open No. 62-60653) or a method in which an amount of a fatty acid or its derivative, such as calcium stearate, to be added into the whole material for constructing an ink tank is reduced to 100 ppm or lower (refer to Japanese Patent Application Laid-Open No. 63-216752).
Even in images formed by an ink-jet recording method, a photograph-like print quality has been recently pursued, and it has thus been required to output a clearer color image. In keeping with such a requirement, various performance characteristics or properties such as excellent coloring ability, and high fastness and water fastness have been required of inks, and performance requirements also have become severe. For example, it is required to make ink droplets ejected minuter, and to enhance the precision of ink-droplet impact on the surface of paper. Accordingly, the influence of substances dissolved out in an ink from members coming into contact with the ink on the ink also becomes more intensified than before. Therefore, the dissolving-out of a trace amount of impurities in an ink, which did not become a problem in the conventional ink-contacting member system, has come up as a new problem.
According to researches by the present inventors, it has been confirmed that when an ink tank using an ink-absorbing member made of a polyolefin is stored at a high temperature or left to stand for a long period of time, the quality of an image formed with an ink contained in the ink-absorbing member is deteriorated. Upon analyzing this problem, the following fact has been become clear. Namely, when the polyolefin is formed into a film or sheet, calcium stearate contained in the polyolefin generally tends to migrate to the surface thereof, and is ease to bleed out. According to the analysis by the present inventors, besides the above, the fact that calcium stearate in the polyolefin becomes easy to be dissolved out in the ink when it is heated has become clear.
When calcium stearate is heated at a temperature exceeding 130xc2x0 C., its crystallinity is decayed, and the crystallinity remains decayed even after the temperature is lowered. When such calcium stearate comes into contact with an ink, it is ion-exchanged by a sodium ion or the like in the ink and dissolved out in the ink. In particular, it has been confirmed that when the polyolefin containing calcium stearate is subjected to a thermal hysteresis at 60xc2x0 C. or higher in a state brought into contact with the ink, calcium stearate becomes easier to be dissolved out. In this state, calcium stearate is dissolved in the ink. Therefore, such problems that the flowability of the ink is impeded do not arise so far as a very great amount of calcium stearate is dissolved out. However, since the ink in which calcium stearate is dissolved is exposed to the air in the vicinity of an ink-ejection orifice, calcium stearate is deposited as impurities about the ejection orifice due to the evaporation of water in the ink. Therefore, when the ink is ejected, a portion of the orifice, to which the impurities have been attached, differs in wettability by the ink from surroundings thereof. As a result, the ejecting direction of the ink is changed, and an ink droplet impacts a position distant from an original position intended to impact, so that the quality of the resulting image (print quality) is deteriorated.
The neutralization reaction of a chlorine compound with calcium stearate, which is a neutralizer, is represented by a reaction scheme
(C17H35COO)2Ca+2HClxe2x86x922C17H35COOH+CaCl2
and hydrochloric acid is neutralized according to such a reaction. Since stearic acid and calcium chloride, which are products by this reaction, exhibit weak corrosive properties, there is a possibility that a new problem may be offered in view of the future trend of ink-jet recording apparatus toward photograph-like printing with high definition and optical density. Therefore, it is desired that such products should not exhibit corrosive properties, if possible.
It is also preferred that, besides the neutralizer, an antioxidant be added to the polyolefin for stabilizing its quality. The antioxidant is added for the purpose of preventing the quality of the plastic from being deteriorated by corrosion or the like by oxidation. The antioxidant may be generally classified into a primary antioxidant and a secondary antioxidant. The primary antioxidant serves to prevent an oxidative deterioration reaction by a radical generated in a polymer from occurring as a chain reaction. Phenolic antioxidants and amine type antioxidants correspond thereto. The secondary antioxidant serves to decompose a peroxide generated in the polymer in such a manner that a radical is not generated. Sulfur-based antioxidants and phosphorus-based antioxidants correspond thereto.
When calcium stearate is added as a neutralizer to a polymer, however, the phosphorus-based antioxidant reacts with this calcium stearate to form calcium phosphate, and this product has a possibility that it may be dissolved out as impurities in an ink, and the impurities may cause a problem of deteriorating the print quality.
On the other hand, as disclosed in Japanese Patent Application Laid-Open No. 62-60653, there is an example in which calcium carbonate, magnesium carbonate or the like is used as a neutralizer in place of calcium stearate. Since the neutralizing action of a carbonate is not very high, however, the amount of the carbonate added becomes greater compared with calcium stearate. In a system using, for example, calcium carbonate, there is also a possibility that products having weak corrosive properties, such as calcium chloride, may be generated like the system using calcium stearate.
Accordingly, it is an object of the present invention to provide ink-contacting members for ink-jet recording apparatus, such as ink-absorbing members, ink tanks and ink-jet cartridges, which have farther an excellent resistance to contact with inks than before and are composed of a polyolefin obtained by using a neutralizer by which an amount to be added may be smaller, and which is chemically stable and does not form any product having a possibility of causing a problem in future even after a catalyst residue is neutralized.
The above object can be achieved by the present invention described below.
According to the present invention, there is thus provided an ink-contacting member used in an ink-jet recording apparatus, which comprises, as a principal component, a polyolefin obtained by adding a hydrotalcite-like compound as a neutralizer.
According to the present invention, there is also provided an ink-absorbing member capable of holding an ink to be fed to an ink-jet head therein, which comprises, as a principal component, a polyolefin obtained by adding a hydrotalcite-like compound as a neutralizer.
According to the present invention, there is further provided an ink tank comprising an ink-absorbing member capable of holding an ink therein, and a case body housing the ink-absorbing member therein and having an opening part communicating with the air, wherein the ink-absorbing member comprises, as a principal component, a polyolefin obtained by adding a hydrotalcite-like compound as a neutralizer.
According to the present invention, there is still further provided an ink-jet cartridge comprising an ink-absorbing member capable of holding an ink therein, an ink tank housing the ink-absorbing member therein, and a printing head for ejecting the ink to be fed from the ink tank, wherein the ink-absorbing member comprises, as a principal component, a polyolefin obtained by adding a hydrotalcite-like compound as a neutralizer.
According to the present invention, there is yet still further provided an ink tank capable of storing an ink to be fed to an ink-jet head, wherein at least a part of the ink tank, with which an ink comes into contact, comprises, as a principal component, a polyolefin obtained by adding a hydrotalcite-like compound as a neutralizer.
According to the present invention, there is also still further provided an ink-jet recording apparatus comprising an ink-contacting member, wherein the ink-containing member comprises, as a principal component, a polyolefin obtained by adding a hydrotalcite-like compound as a neutralizer.